1. Field of the Invention
The present invention relates generally to biodegrading volatile organic compounds found in refinery liquid waste streams and, in particular, to a process and apparatus for removing volatile organic compounds from refinery liquid waste streams.
Processes for biodegrading hazardous organic waste are generally classified in U.S. Patent Office Class 435/262.5.
2. Description of the Related Art
Microbial degradation of oil dates back to at least 1942, when the American Petroleum Institute began to subsidize research in the field. Considerable basic knowledge about factors that affect natural biodegradation, about the kinds of hydrocarbons capable of being degraded, and about the species and distribution of the microorganisms involved in biodegradation had already been developed in the early 1970s. The Office of Naval Research sponsored more than a dozen basic and applied research projects in the late 1960s and early 1970s on oil biodegradation to control marine oil spills. Since this time, a large number of refineries, tank farms, and transfer stations now employ in situ bioremediation to restore land contaminated by accidental spills of fuel oil or other hydrocarbons.
The microorganisms so employed are capable of assimilating and breaking down non-soluble organic materials including hydrocarbons that convert grease and oil into relatively harmless substances of water-soluble products, carbon dioxide and a lesser quantity of fatty acids.
Oil refineries create liquid waste streams which can be difficult to clean up. Oily water sewers can contain dissolved volatilizable components which under ambient conditions emit volatile organic compounds (VOCs), e.g., benzene, as a vapor effluent. At least a portion of these VOCs must be removed or otherwise treated to conform to environmental regulations. Typically, such vapor effluents are treated by passing them through activated granulated charcoal filters which adsorb volatile hydrocarbons. However, removing the bulk of volatile hydrocarbons by this technique can be costly inasmuch as filters require frequent replacement.
Accordingly, it would be desirable to treat these vapor streams by removing most of the volatile organic compounds with an alternate technique which can be carried out at less expense and using activated granulated charcoal filters to remove any residual volatile organic compounds.
U.S. Patent Document H1,337 to Hoeppel discloses a biodegradation apparatus for treating contaminated soil which comprises an enclosed vessel through which is passed moistened air to remove volatile hydrocarbons from the soil. The outgoing air is supplied to a vapor phase bioreactor, e.g., a biofilter of granular activated carbon, for removal of hydrocarbon contaminants and thence to a conventional granular activated carbon filter to absorb remaining hydrocarbon contaminants.
U.S. Pat. No. 5,942,552 to Cox discloses microbiological fire-fighting formulation which comprises a bioremediating component such as Bacillus subtilis, surfactants, foaming agents, and inorganic nutrients.
U.S. Pat. Nos. 4,482,632 and 4,288,545 disclose microbiological strains which can be used to decompose organic compounds.
U.S. Pat. No. 5,232,596 to Castaldi discloses a slurry-phase bioremediation treatment of organic sludge by dissolving the contaminants into an aqueous phase and microbially degrading them. The process recirculates off-gas components such as benzene, toluene, xylenes, and naphthalene from the system back to one or more of the bioreactors, to return high volatility toxic constituents for increased microbial degradation and control of volatile toxic constituent emissions from the process.
In one aspect, the present invention relates to a process for reducing volatile organic compound content of a liquid refinery waste stream which can be integrated into an oil refinery process scheme. The process comprises exposing a liquid refinery waste stream comprising dissolved volatile organic compounds to conditions which volatilize the organic compounds to provide a waste vapor stream, contacting the waste vapor stream, preferably in a single pass, with an aqueous liquid medium containing volatile organic compound-metabolizing microbes under volatile organic compound-metabolizing conditions. Such contacting provides a treated waste vapor stream containing volatile organic compound metabolization products and reduced volatile organic compound content which can be further processed by passing said treated waste vapor stream through a volatile organic compound absorbing filter.
In another aspect, the present invention relates to an apparatus for reducing hydrocarbon content of a liquid refinery waste stream comprising dissolved volatile organic compounds which are volatilizable to provide a waste vapor stream. The apparatus comprises:
a) a receptacle having an inlet for introducing to the receptacle the refinery waste vapor stream which contains volatile organic compounds, an aqueous liquid medium containing hydrocarbon-metabolizing microbes, a means for contacting said aqueous liquid medium with said refinery waste vapor stream under hydrocarbon-converting conditions to provide a treated stream containing hydrocarbon decomposition products and reduced hydrocarbon content, and an outlet for removing said treated stream therefrom to the atmosphere or a filtering means. Thus the apparatus can further comprise b) a filtering means which contains an inlet connected to the outlet of said receptacle, a filtering element, and an outlet for passing a filtered product of further reduced hydrocarbon content (as compared to the treated stream from a)).
In yet another aspect, the present invention relates to a method of extending the life of an adsorbent which is used to adsorb volatile organic compounds in a vapor stream derived from a liquid refinery waste stream. The process comprises
i) exposing said liquid refinery waste stream to conditions sufficient to volatilize VOCs dissolved therein to provide a vapor stream;
ii) contacting the vapor stream in a single pass with an aqueous liquid medium containing volatile organic compound-metabolizing microbes under volatile organic compound-metabolizing conditions to provide a treated stream containing volatile organic compound metabolization products and reduced volatile organic compound content; and
iii) contacting the treated stream with the adsorbent.